1. Field of the Invention
The present invention relates to a portable electronic equipment with such a structure of a portable terminal such as, for example, a portable telephone, PHS, a cordless telephone, a handy game gear, etc., having button keys adapted to be pushed in to operate, and in particular, it relates to a button key's structure capable of reducing stresses on a board received in a casing.
2. Description of the Related Art
For a typical example of portable electronic equipment of the above kind, there has been well known a portable telephone, an example of which is illustrated in FIGS. 10(a) and 10(b), FIG. 11 and FIG. 12. FIGS. 10(a) and 10(b) are a front elevational view and a side view, respectively, of the conventional portable telephone; FIG. 11 is an enlarged cross sectional view taken along line A—A, showing a structure of a key switch employed in the portable telephone; and FIG. 12 is an enlarged plan view of the key switch, showing a button key and a button key seat thereof.
The portable telephone 110 as illustrated in FIGS. 10 through 12 has a outer housing or casing comprising a front case 111 and a rear case 112 detachably assembled with each other, and a circuit board 12 for radio signal transmission and reception accommodated in the casing with an antenna 116 being projected from the casing. In this case, the cases 111, 112 are integrally connected with each other by means of fitting engagement using concavo-convex engagement between concaves and convexes, or engagement recesses and protrusions, or by means of screws. Also, on the surface of the front case 111, there are provided an LCD (liquid crystal display) 113, a microphone 114, a receiver 115, and a plurality of key switches 117. In this case, each key switch 117 includes a button key 118 ordinarily formed of ABS or the like and a button key seat 119 ordinarily formed of silicon rubber or the like. Each button key 118 is formed on a periphery of near-bottom portion thereof with a flange 125 extending slightly radially outwards from a side surface thereof.
The circuit board 129 built in the portable telephone 110 is provided on its surface opposite the button keys 118 with a key seat 123 and a plurality of elastic plate-shaped switch contacts in the form of click plates 122 at locations corresponding to the positions of the button keys 118. On a surface of the circuit board 129 facing the rear case 112 there are mounted electronic components 121 such as LSIs, silicon chips and the like. With such a construction, when a button key 118 is depressed or pushed in for purposes of dialing or the like, the button key seat 119 together with the depressed button key 118 is caused to move downwards, pressing the corresponding click plate 122 for switching operation.
In this case, an upward movement of each button key 118 is limited by the flange 125 thereof which is placed into abutting engagement with the rear or inner surface of the front case 111, but there is no such a limitation on a downward movement of each button key 118. Thus, as a button key 118 is being pushed in more and more, it is caused to move further in the downward direction with the result that the circuit board 129 is subjected to an increasing stress. On the other hand, recently used portable electronic with equipment such as portable telephones and the like, the thickness of a circuit board is becoming thinner for the purpose of reducing the weight and size thereof, so many of them have a thickness of 0.6 mm or below. As a result, the circuit board 129 is more and more liable to be subjected to frequent stresses upon manipulation of the button keys 118 or the like, which is undesirable from the point of view of durability.
With the conventional portable electronic equipment described above, there are employed a lot of button keys 118 of which movements in their returning direction are limited to a certain stroke. However, there is no limitation to their movements in a depressing direction, so the larger a thrust or pressing force applied to a button key 118, the greater stress will be given to the circuit board 129 inside the cases 111, 112. Moreover, the circuit board 129 accommodated in the cases 111, 112 is becoming thinner (e.g., the thickness of 0.6 mm being in the mainstream) and hence weakened against stress according to a downsizing of the portable electronic equipment. For these reasons, with the portable electronic equipment in which the button keys 118 are frequently operated, there is a fear that frequent deformations or warpings of the circuit board 129 might cause cracks in soldered portions of the electronic components mounted on the circuit board 129 or breakage of such electronic components.
In this regard, to prevent the deformation or warpage of the circuit board 129 according to the repeated pushing or pressing operations to the button keys 118, it might be considered that unillustrated bosses are provided on the rear case 112 which is in contact with the back side of the circuit board 129. However, it is substantially impossible to provide such bosses at the locations corresponding to the back side portions of all the button keys 118.